This proposal describes a program directed towards the chemical synthesis of several naturally occurring bacterial modulation signals of the legume- rhizobium factor family (e.g. 1 and 2) and a number of natural oligosaccharide ligands of selectins (e.g. 3 and 4). Furthermore this program includes molecular design, chemical synthesis and biological evaluation of analogs of the above mentioned natural compounds. Finally, the design and synthesis of novel oligosaccharide molecules, as specific compounds or combinational libraries, is proposed. The proposed research is expected to have significant implications in chemistry, biology, and medicine, particularly in the areas of nitrogen fixation, neutrition, and inflammation.